Type I Alveolar Epithelial Cells Mount Innate Immune Responses during Pneumococcal Pneumonia

Abstract

Pneumonia results from bacteria in the alveoli. The alveolar epithelium consists of type II cells, which secrete surfactant and associated proteins, and type I cells, which constitute 95% of the surface area and met anatomic and structural needs. Other than constitutively expressed surfactant proteins, it is unknown whether alveolar epithelial cells have distinct roles in innate immunity. Since innate immunity gene induction depends on NF-κB RelA (also known as p65) during pneumonia, we generated a murine model of RelA mutated throughout the alveolar epithelium. In response to LPS, only 2 of 84 cytokine transcripts (CCL20 and CXCL5) were blunted in lungs of mutants, suggesting that a very limited subset of immune mediators is selectively elaborated by the alveolar epithelium. Lung CCL20 induction required epithelial RelA regardless of stimulus, whereas lung CXCL5 expression depended on RelA after instillation of LPS but not pneumococcus. RelA knockdown in vitro suggested that CXCL5 induction required RelA in type II cells but not type I cells. Sorted cell populations from mouse lungs revealed that CXCL5 was induced during pneumonia in type I cells, which did not require RelA. TLR2 and STING were also induced in type I cells, with RelA essential for TLR2 but not STING. To our knowledge, these data are the first direct demonstration that type I cells, which constitute the majority of the alveolar surface, mount innate immune responses during bacterial infection. These are also the first evidence for entirely RelA-independent pathways of innate immunity gene induction in any cell during pneumonia.

CXCL5-secreting pulmonary epithelial cells drive destructive neutrophilic inflammation in tuberculosis

“…Platelets and endothelial and epithelial cells can secrete CXCL5 (31,39,41). Our experiments revealed that upon in vitro M. tuberculosis infection, only AECII produced CXCL5, while CXCL2 was secreted by PMNs and BMDMs, and CXCL1 was secreted by BMDMs and AECII.…”

“…Experiments with BM chimeric mice and MACS-sorted lung cells confirmed and extended our in vitro and in situ findings that CXCL5-dependent PMN recruitment was exclusively driven by radioresistant lung-resident cells and not by radiosensitive hematopoietic cells. CXCL5 expression is neither cell type nor organ specific but, rather, is expressed by diverse tissue-resident cells, including car- diac myocytes (57), alveolar epithelial cells (31,41), enterocytes (38), aortic endothelial cells (58), and kidney tubular cells (E. Disteldorf and C. Krebs et al, unpublished observations). This broad expression emphasizes the general role of CXCL5-secreting resident tissue cells in orchestrating PMNs in response to microbial and inflammatory danger signals (6).…”

“…CXCL15, which is produced by bronchial epithelial cells (29), contributes to pulmonary defense against K. pneumoniae infection (37). CXCL5, which plays a role in LPS-induced lung inflammation, is secreted by type I and type II alveolar epithelial cells (AECI and AECII, respectively) (31,(38)(39)(40)(41). During M. tuberculosis infection, CXCR2 and its ligand CXCL5 are strongly upregulated in lungs (9,42,43).…”

Expression of Piwi protein MIWI2 defines a distinct population of multiciliated cells

“…The lavage fluid was centrifuged at 300 g for 5 minutes at 4°C, and cell pellets were used for differential counts. BALF cell counts were performed as previously described (39), with cytocentrifuged slides stained with the Diff-Quik staining kit (Dade Behring) after counting of suspended cells using a hemocytometer. For BALF cytokine measurement, the supernatant of the first 1-ml lavage sample was saved separately at -80°C for protein analysis by ELISA (R&D Systems).…”

Differentiation of Mouse Induced Pluripotent Stem Cells Into Alveolar Epithelial Cells In Vitro for Use In Vivo

“…The first step in regenerative medicine for end-stage lung diseases is generation of alveolar epithelium containing two cell types: alveolar epithelial type I and type II cells (AEC I and II). AEC I cells are large, flattened cells that make up 95% of the alveolar lining area and are responsible for gas exchange, whereas AEC II cells are cuboidal cells, more abundant but smaller than AEC I cells, that make up 5% of the alveolar lining area [1,2]. AEC I cells are terminally differentiated, unable to replicate, and susceptible to environmental toxicants and pathogens.…”